Reproduction of a good quality print image from an original color photograph or picture depends on the color separation. Color separation is a process in which the original color picture is passed through blue, green and red filters respectively to produce cyan, magenta, yellow and black separations. Masking, a process to adjust differences between the original color and the ink color of the print, is also carried out. As compared to the optical camera separations in the traditional method, the scanner translates the highlight and shadow areas of the color original into electrical signals to carry out separations and masking while adjusting color tones and, at the same time, adjusting the magnification. Original images are recorded by the modulation of the quantity of light from a light source, such as a laser or glow lamp, but the modulation characteristic in the quantity of such light is generally not linear. Also, for a laser, time-oriented changes in the quantity of light are unavoidable.
An analog feed-back control system of continuous operation has been employed. This system, however, has such disadvantages as temperature drift due to the analog system, so that control is not possible during high-speed recording because the time delay is dependent on the modulation characteristic of the light source and because of difficulty in correcting non-linear modulation characteristic.